Antenna system for vhf and uhf radio direction finders

ABSTRACT

An antenna system for a VHF and UHF radio direction finder comprises a loop antenna formed by turns which are arranged on an elongated magnetodielectric core. The antenna system has also an omnidirectional antenna member and a switch means which shapes the resultant directivity pattern by adding up signals from the loop and omnidirectional antennas and changing the position of this pattern discretely by 180* in the horizontal plane to obtain its mirror image. The omnidirectional antenna is made in the form of a closed turn arranged on the core of the loop antenna so that it is substantially perpendicular to the turns of the loop antenna. A portion of the closed turn is disposed in the direction of the longitudinal axis of the core is elevated above the core surface through a known distance whereby the magnitude of the signal from the omnidirectional antenna is such that the two resultant directivity patterns of the antenna system intersect only at two points in a horizontal plane.

United States Patent (191 Bukhman et al.

[ 1 March 6, 1973 154] ANTENNA SYSTEM FOR VHF AND UHF RADIO DIRECTION F INDERS [22] Filed: Nov. 3, 1971 [21] Appl.No.: 195,301

[52] U.S. Cl. ..343/788, 343/120, 343/855 [51] Int. Cl. ..G01s 5/04 [58] Field of Search ..343/120, 787, 788, 855

[56] References Cited UNITED STATES PATENTS 3,588,900 6/1971 Salmet ..343/l20 3,495,264 2/1970 Spears ..343/788 Primary ExaminerEli Lieberman [5 7] ABSTRACT An antenna system for a VHF and UHF radio direction finder comprises a loop antenna formed by turns which are arranged on an elongated magnetodielectric core. The antenna system has also an omnidirectional antenna member and a switch means which shapes the resultant directivity pattern by adding up signals from the loop and omnidirectional antennas and changing the position of this pattern discretely by 180 in the horizontal plane to obtain its mirror image. The omnidirectional antenna is made in the form of a closed turn arranged on the core of the loop antenna so that it is substantially perpendicular to the turns of the loop antenna. A portion of the closed turn is disposed in the direction of the longitudinal axis of the core is elevated above the core surface through a known distance whereby the magnitude of the signal from the omnidirectional antenna is such that the two resultant directivity patterns of the antenna system intersect only at two points in a horizontal plane.

2 Claims, 3 Drawing Figures ANTENNA SYSTEM FOR VHF AND UHF RADIO DIRECTION FINDERS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION DESCRIPTION OF PRIOR ART Widely known in the art are antenna systems of medium-wave direction finders which comprise a loop antenna formed by conductor turns arranged on a magnetodielectric core, an omnidirectional antenna and a switch designed for shaping the resultant directivity pattern by adding the signals from the loop and omnidirectional antennas and varying the position of this pattern in the horizontal plane discretely by 180 to obtain its mirror image.

The loop antennas in such antenna systems are equipped with a rotating mechanism and have a directivity pattern shaped as a figure-of-eight. To obtain a cardioid directivity pattern which is required for normal operation of the antenna system of a radio direction finder the signal from the loop antenna is summed with the signal from the omnidirectional antenna which is mounted in a fixed position at some distance from the loop antenna.

However, such antenna systems are not suitable for use at very high and ultrahigh frequencies as the signals from the loop and omnidirectional antennas come to the switch in arbitrary phases, which phases at such frequencies may differ greatly and depend on the relative position of the above antennas with respect to the source of the signal. Owing to this the signals cannot be added up in the same phase (or in phase opposition) Another disadvantage of the existing omnidirectional antennas is that they are rather bulky because of their height and, therefore, cannot be combined in a smallsize rotating assembly together with a loop antenna.

SUMMARY OF THE INVENTION An object of the present invention is to provide an antenna system for a VHF and UHF radio direction finder in the form of a simple small-size rotating assembly with a resultant directivity pattern enabling such an antenna system to be used within a wide range of very high and ultrahigh frequencies.

With this object in view, in the antenna system for a VHF and UHF radio direction finder comprising a loop antenna formed by turns arranged on a magnetodielectric core, an omnidirectional antenna and a switch designed for shaping the resultant directivity pattern by adding up the signals from the loop and omnidirectional antennas and changing the position of this pattern discretely by 180 in the horizontal plane to obtain its mirror image, the omnidirectional antenna, according to the invention, is made in the form of a closed turn arranged on the loop antenna magnetodielectric core so that it is roughly perpendicular to its turns; one portion of said closed turn is located along the longitudinal axis of the core and elevated above the core surface through a distance at which the magnitude of the signal from the omnidirectional antenna is such that the two resultant directivity patterns of the antenna system intersect only at two points in the horizontal plane.

It is preferable that the elevated portion of the 'om nidirectional antenna should be in the form of a conductive band which is connected to conductive strips mounted on a dielectric substrate attached to the loop antenna core.

The antenna system described herein is simple in construction and has small dimensions and weight.

BRIEF DESCRIPTION OF THE DRAWING The invention will be best understood from the following description of its specific embodiment when read in conjunction with the accompanying drawings in which:

FIG. 1 is the general view of the antenna system including a switch for a VHF and UHF radio direction finder, according to the invention;

FIG. 2 is a bottom view of same minus the system in FIG. 1, without the switch;

FIG. 3 is a schematic diagram of the antenna system for a VHF and UHF radio direction finder.

DESCRIPTION OF PREFERRED EMBODIMENTS According to the invention the antenna system for a VHF and UHF radio direction finder comprises a loop antenna 1 (FIG. 1) made up of ten individual turns 2 arranged on an H-shaped magnetodielectric core 3 connected in parallel by bridges 4 (FIG. 2). Said bridges 4 are provided with leads 5 and 5' which are connected to the bridges in the space between the fifth and sixth turns 2. The antenna system also comprises an omnidirectional antenna 6 (FIG. 1) in the form of a closed turn enveloping the core 3 of the loop antenna I. Said closed turn is arranged in a position normal to the turns 2 of the loop antenna 1.

One portion of the omnidirectional antenna 6 located along the longitudinal axis of the core 3 is elevated above the turns 2 of the loop antenna 1 and is shaped as an arc. The distance from the apex of said are to the surface of the core 3 is equal to two to three times the thickness of the core 3 of the loop antenna 1. This is necessary in order that the efficiency of the omnidirectional antenna 6 should not be less than that of the loop antenna 1.

Structurally, the elevated portion of the omnidirectional antenna 6 is designed as follows: a conductive band is deposited on a rectangular dielectric substrate 7 made of arc-shaped acrylic material. To increase the capacitance of the antenna 6 five conductive strips 8 are additionally deposited on the substrate 7. The strips 8 are arranged and spaced uniformly along the length of the substrate 7 and are perpendicular to the conductive band of antenna 6. The length of the strips 8 is equal to the width of the substrate 7.

The conductive band and the strips 8 are formed on the surface of the substrate 7 with the help of a conductive paint or by copper-foil printing techniques.

The dielectric substrate 7 is rigidly attached to the core 3 of the loop antenna 1 so that the conductive band should lie in a plane perpendicular to the turns 2 of the loop antenna 1. The ends of the conductive band which forms part of the closed turn of the omnidirectional antenna 6 are connected to a shorting wire 9, the middle portion of which is connected to a lead 10 (FIG. 2) of the omnidirectional antenna 6.

The loop antenna 1 (FIG. 1) with the omnidirectional antenna 6 attached to it is mounted on a casing of the switch 11. The casing of the switch 11 is a shielded metal sleeve 12 housing a printed board on which all circuit elements of the switch are mounted. In the antenna system for a VHF and UHF radio direction finder, according to the invention, the leads (FIG. 3) and 5' of the loop antenna 1 are connected to a voltage divider formed by capacitors 13, 14 and resistors 15, 16. A midpoint 17 of said voltage divider is grounded. At the same time the leads 5 and 5' are connected to an output 22 of the antenna system through capacitors l8, l9 and diode gates 20, 21, respectively, the diodes 20 and 21 being connected in opposition. The junction points between the capacitor 18 and the diode 20, and between the capacitor 19 and the diode 21 are interconnected by decoupling chokes 23 and 24 and provided with a lead 25. The lead 25 is grounded through a by-pass capacitor 26.

The junction point between the diodes 20 and 21 is also grounded through a decoupling choke 27.

The lead of the omnidirectional antenna 6 is connected to the output 22 of the antenna system through a phasing choke 28 and a resistor 29.

The antenna system described herein operates as follows. An L.F. voltage which controls operation of the switch 11 is applied to the lead 25. When the loop antenna 1 picks up a radio signal, two equal but out of phase voltages with respect to earth appear at its leads 5 and 5' due to the action of the voltage divider formed by the resistors 15, 16 and the capacitors 13, 14. These voltages are applied to the output 22 of the antenna system through the blocking capacitors 18, 19 and the diode gates and 21 which switch the LR voltage. On a positive half-cycle of the controlling L.F. voltage the diode 21 is conducting while the diode 20 is cut off,

. and the voltage from the lead 5' of the loop antenna 1 is applied to the output 22 of the antenna system in one phase. On a negative half cycle of the controlling L.F. voltage the diode 20 is rendered conductive and voltage is applied to the output 22 of the antenna system from the lead 5 of the loop antenna 1, this voltage being in phase opposition to the previous voltage. At such time the diode 21 is non-conducting.

Therefore, depending on the polarity of the controlling L.F. voltage, the voltages alternately out of phase by 180 are applied to the input 22 of the antenna system from the leads 5 or 5 of the loop antenna 1.

Simultaneously the signal from the omnidirectional antenna 6 is also applied to the output 22 of the anten- 'na system through the phasing choke 28 and the resistor 29. At the output 22 the signals from the omnidirectional antenna 6 and the directional antenna 1 are added up. As a result, the horizontal directivity pattern resulting from the addition of these signals closely resembles a cardioid. Depending on the polarity of the controlling L.F. voltage the resultant directivity pattern changes its position in the horizontal plane by 180, so

that actually two directivity patterns are produced, which are mirror images of each other and which intersect only at two points.

When mounted on a rotating mechanism the antenna system described herein can be used in an automatic radio compass or a direction finder operating in the very-high and ultrahigh frequency ranges. Owing to its small size the antenna system is suitable for use in airborne automatic radio compassesor direction finders of other mobile ob ects such as ships and ground vehicles.

Besides, when mounted in a fixed position on a mobile object the antenna system can be used with VHF and UHF fixed-loop radio compasses designed for homing the mobile object on a radio station.

The antenna system described herein retains its directivity patterns suitable for direction finders which depend for their operation on amplitude comparison, within a wide frequency range from to 260 MHz which can be extended down to 20 MHz by readjusting the phasing elements.

The operating frequency range of this antenna system covers both international distress frequencies 121.5 and 243 MHz and, therefore, complies with the relevant requirement of the International Civil Aviation Organization. The antenna system described herein may also be used in various search operations.

What is claimed is:

1. An antenna system for a VHF and UHF radio direction finder comprising: a loop antenna having a core member with a longitudinal axis, and turns of said loop antenna wound on said core member so as to be spaced along said longitudinal axis an omnidirectional antenna which includes an elongated conductor disposed to lie in a plane substantially perpendicular to said turns of the loop antenna, said plane passing through the longitudinal axis of said core member; a switch means for shaping a resultant directivity pattern by adding up signals from said loop antenna and said omnidirectional antenna and varying the position of said directivity pattern discretely by in a horizontal plane to obtain a mirror image of said directivity pattern; conductor means for forming a closed turn of said omnidirectional antenna disposed on said core member, a portion of said closed turn being located along said longitudinal axis and elevated above the core surface through a known distance whereby said directivity pattern and said mirror image thereof intersect only at two points in a horizontal plane.

2. An antenna system as of claim 1, wherein the elevated portion of said omnidirectional antenna is constituted by said elongated conductor made in an arcuate form, said elongated conductor including transverse conductive strips arranged on a dielectric substrate attached to said core member of said loop antenna. 

1. An antenna system for a VHF and UHF radio direction finder comprising: a loop antenna having a core member with a longitudinal axis, and turns of said loop antenna wound on said core member so as to be spaced along said longitudinal axis ; an omnidirectional antenna which includes an elongated conductor disposed to lie in a plane substantially perpendicular to said turns of the loop antenna, said plane passing through the longitudinal axis of said core member; a switch means for shaping a resultant directivity pattern by adding up signals from said loop antenna and said omnidirectional antenna and varying the position of said directivity pattern discretely by 180* in a horizontal plane to obtain a mirror image of said directivity pattern; conductor means for forming a closed turn of said omnidirectional antenna disposed on said core member, a portion of said closed turn being located along said longitudinal axis and elevated above the core surface through a known distance whereby said directivity pattern and said mirror image thereof intersect only at two points in a horizontal plane.
 1. An antenna system for a VHF and UHF radio direction finder comprising: a loop antenna having a core member with a longitudinal axis, and turns of said loop antenna wound on said core member so as to be spaced along said longitudinal axis ; an omnidirectional antenna which includes an elongated conductor disposed to lie in a plane substantially perpendicular to said turns of the loop antenna, said plane passing through the longitudinal axis of said core member; a switch means for shaping a resultant directivity pattern by adding up signals from said loop antenna and said omnidirectional antenna and varying the position of said directivity pattern discretely by 180* in a horizontal plane to obtain a mirror image of said directivity pattern; conductor means for forming a closed turn of said omnidirectional antenna disposed on said core member, a portion of said closed turn being located along said longitudinal axis and elevated above the core surface through a known distance whereby said directivity pattern and said mirror image thereof intersect only at two points in a horizontal plane. 